1. Field of the Invention
The present invention relates to an inter-process buffer controlling apparatus and method in which the size of an inter-process buffer for storing work subjects of a process is varied in a system in which a work is done through a plurality of processes, as well as to a program and a storage medium for realizing such an apparatus and a method.
2. Description of the Related Art
The Kanban System is known as a typical conventional system for reducing the number of in-process items. In this system, the number of in-process items is minimized because each process is executed in accordance with requirements that are given by the following process.
In this system, desired production is attained and the capacity utilization ratios of respective processes are kept high if tact balance among the processes is kept and the number of items being processed is relatively stable. However, in large-item-small-scale, custom-manufacturing production lines, the capacity utilization ratio and the production per unit time of a process concerned may lower to a large extent because not only a variation in actual tact time but also other various variations such as variations in amount and time due to the demand of customers and a variation relating to collection of parts occur depending on a product mix at each time. The term “actual tact time” means actual work time that is taken for each product in the process concerned rather than man-hours that is in proportion to the number of operators. The term “product mix” means a combination of products including their proportion and flowing order.
The TOC (theory of constrain) and the DBR (drum buffer rope) methods are known as methods for solving the above problems.
In these methods, inputting items to a production line in accordance with the capacity of a process (bottleneck process) having a lowest manufacturing capacity in the process prevents manufacture of unnecessary in-process items. And production is maintained by providing, at proper positions, a buffer having a certain capacity which prevents further reduction in the capacity of the bottleneck process due to suspension or a slowdown of operation that is caused from variations.
Incidentally, in the above conventional methods, a bottleneck process itself is not fixed and in many cases production is not maintained satisfactorily in the case where the product mix or the demand of customers varies to a large extent.
Further, in recent years, for many of products as subjects of large-item-small-scale production, shortening of a manufacturing period has come to be required strictly and the estimation of demand has become more difficult.
Therefore, not only a measure to minimize loss of variations in demand but also a measure to accommodate needs of customers should be provided urgently. A technique for further reducing the number of in-process items and actual process time with reliability without hindering reduction in the manufacturing cost is desired strongly. The term “actual process time” means time that is taken actually from a start to an end of each process and may include a time during which no work is done actually.